How to allow blender to only use part of your CPU computing power?
Under render > Performance >Threads,
set it to fixed and you can chose how many Cores Blender can use when rendering in cycles. Not sure for Eevee. This should also work for modeling 



Also you can use Cpu affinity which limits how mnay core blender uses as a whole through 

Task manager> Details>Blender.exe (Might be different I use .zip) > right click > Set affinity  ,  on windows

or using what is discussed here for Ubuntu Link to Ubuntu forums

Note: For this to work you will have to make sure the amount of threads in performance is the same as the amount of cores as you have set in the affinity, or it will be reset every time you go into rendered view or render.